Physicians have been treating cancerous liver tumors that are up to about five centimeters in diameter using numerous methods including electrosurgery, cryosurgery, and ethanol injection. Another option for treating liver tumors is the application of intense ultrasound energy (IUS). Investigators have been developing IUS devices and methods for several years, especially for treating diseased tissue in the prostate gland and liver. The frequency regime for IUS devices is generally in the range of 1–30 MHz. An inherent challenge when using IUS is maintaining a focused beam of acoustic energy from the ultrasonic energy transfer element onto the diseased tissue for a sufficient number of seconds to raise the temperature of the tissue high enough (at least 43 degrees C.) to cause tissue necrosis. It is then necessary to move the focus of the beam, which may be the size of a grain of rice, to a new, adjacent location to continue the ablation process. These steps are repeated until the entire volume of diseased tissue has been ablated. The time required to effectively treat this volume of tissue with IUS may exceed 20–30 minutes. It is critical, therefore, that the relative movement between the IUS energy transfer element and the tissue being treated is small to ablate selectively the tumor and a desired margin of healthy tissue in minimal time. During procedures for destroying diseased tissue within the liver, the physician must contend with movement of the liver due to the patient's breathing and the heart beating. When the diseased tissue is a cancerous tumor, it is obviously critical that as much of the cancerous cells as possible be destroyed to achieve the maximal therapeutic effect and to lengthen the patient's life.
Methods for stabilizing organs or for compensating for organ movement during medical procedures are well known in the art. For example, stabilization devices and methods developed for beating heart surgery include compression and/or vacuum attachment to immobilize a portion of heart while suturing together blood vessels. Enclosed platforms or dome-like structures for creating a workspace for endoscopic access and visualization have also been devised for vein harvesting and cardiac surgery. In addition, electrodes that attach to the skin of the patient for diagnoses or therapy of underlying tissue are also well known. These include electromyography (EMG) electrodes for monitoring muscular activity or functional electrical stimulation (FES) electrodes for stimulating muscular contraction. These electrodes move freely with the movements of the patient, thus minimizing relative movement between the electrode and the relevant tissue.
External, non-invasive IUS instruments developed for liver treatment require sufficient energy to offset losses of energy through the abdominal wall and to compensate for the movement of the liver. An alternate approach is to introduce a therapeutic IUS energy transfer element through a small incision in the abdomen and to attach it directly to the surface of the liver, and allow the energy transfer element to “ride” with the movement of the liver during the treatment. For example, a physician would position the IUS treatment energy transfer element on the anterior surface of the liver near a tumor with the aid of an intracorporeal, ultrasonic imaging device. The same imaging device would provide monitoring data to a control system in order to develop a “tool path” program for the energy beam focus. Then using electronic and mechanical focusing/directioning means, the IUS treatment energy transfer element would automatically ablate the tumor as the physician monitored the progress displayed on the control system.
Sometimes it is necessary to position the IUS energy transfer element apart from the organ surface so that the underlying tissue to be treated is in the focal range of the energy transfer element. Therefore, the IUS energy transfer element may be enveloped in a fluidic media such as, for example, a saline solution, having relatively the same acoustic energy transmission characteristics as the underlying tissue to provide acoustic coupling between the energy transfer element and the tissue. Also the IUS energy transfer elements generate a significant amount of heat. Since the efficiency of the IUS energy transfer element may decrease rapidly with temperature increase, the fluidic media also serves as a coolant for the energy transfer element. Devices having a water-filled balloon attached over the IUS energy transfer element, and maintained with a fresh water flow, have been effectively devised primarily for these purposes.
A multi-element, linear array IUS energy transfer element transmits acoustic energy from the energy transfer element face in an approximately two-dimensional plane, focusing at some distance away from the energy transfer element face. The focal depth and angular directivity within that plane of the focus may be set by the type of acoustic lens attached to the face of the energy transfer element, or electronically controlled within certain ranges. It may also be necessary, however, to physically move the energy transfer element to position the acoustic focus. For example, the energy transfer element may be rotated on its longitudinal axis to sweep the acoustic plane through a volume sector. It may also be vertically adjusted closer or nearer to the tissue.
What is needed, therefore, is a medical device that attaches directly to an internal bodily organ and moves freely with the movement of the organ in order to minimize the relative motion between the energy transfer element and the organ during treatment of underlying tissue. What is further needed is such a medical device that also incorporates energy transfer element coupling, cooling, and orienting/positioning means. What is further needed is also such a medical device that may be used minimally invasively on a surgical patient. The present invention addresses these needs and overcomes numerous deficiencies of the prior art.